Known equipment to humidify gas turbine inlet (i.e., combustion) air for performance augmentation have included one or the other of the systems described below. These systems are generally used under high load conditions and relatively high ambient temperatures (over about 40.degree. F.).
An evaporative cooler system includes an absorbtive media or other system located in a low velocity section of the air intake duct, and is supplied with water which is exposed to the air flowing through the media for evaporation of the water by energy in the air. The energy used for evaporating the water reduces the temperature of the air to near the saturation point, or wet bulb temperature. The reduced temperature of the air entering the gas turbine compressor increases the gas turbine temperature ratio and mass flow, thereby increasing gas turbine output and efficiency. This system does not have the ability to supersaturate the combustion air, however, without the potential for large water drop entrainment which potentially erodes the compressor blades.
An inlet fogging system includes a plurality of manifolds and nozzles that spray finely atomized water into the combustion air for the gas turbine. The fogging systems are located in the air intake duct and have the ability to humidify air to (or near) the saturation point and in most applications to supersaturate the air. Supersaturation of the air in the duct leads to the potential for the formation of large water drops that can erode compressor blades. Condensation of water in the intake duct also requires a drain system to dispose of the unwanted water. Water entrained in the air entering the compressor does cool the air being compressed to reduce compressor power consumption and thereby increase gas turbine power output. Inlet foggers are difficult to control, however, since measurement of supersaturation is impossible.
A compressor intercooling system involves cooling of air between sections of an air compressor, reducing the compressor power consumption and thereby increasing gas turbine power output. Cooling of the air by intercoolers have included (1) heat exchangers where energy removed from the air is rejected to an external media; and (2) evaporative intercoolers in which water is evaporated into the air being compressed. Heat exchanger type intercoolers remove energy from the gas turbine system which must be replaced by energy from fuel burned, so they significantly decrease efficiency, albeit they do increase power output. Evaporative intercoolers perform essentially the same function as inlet air supersaturation, but evaporative intercooling is performed in interstage pressure vessels, which are costly and which introduce pressure drops which degrade gas turbine performance. Moreover, intercooling systems typically must be used under all operating conditions.